Vehicle Notes

The Base Vehicle for Argonaut

The Traxxas E-Maxx is possibly the most popular choice of models
for off-road robots that are based on a commercial RC vehicle.
The E-Maxx is a very popular vehicle in the RC world and so there are
plenty of used vehicles available on eBay and also plenty of aftermarket parts.
However, the E-Maxx may not be the best type of vehicle for off-road
robotics.

The niche hobby of RC Rock Crawling probably most-closely matches what
an off-road robot is supposed to do: navigate unknown terrain and maintain
traction. These crawler vehicles have articulation that allows the fixed
axles to conform to the terrain they traverse. Unfortunately, there are not
many commercial crawler models available.
The Axial AX10 Scorpion (seen to the right) is one of the few.

Ultimately my budget dictated my choice of vehicles. The Argonaut project
is an attempt to do as much as possible using as little money as possible.
So I pulled my 21 year old Kyosho Ultima out of its box in the closet.

I actually switched from the carbon fiber race chassis back to the original
aluminum channel chassis (seen in the picture) because its tub shape allows
me to bolt on a flat piece of material as a deck.

I could not find a properly-ratioed gearmotor, so I picked the stock RC car
motor and found a small pinion gear. The standard pinion gear had 15 teeth,
the smaller one has 9 teeth, so I reduced my speed and increased torque by 60%.

I bought a set of front and rear HPI rims at my local hobby shop.
But I got my HPI Yokohama Geolandar tires from a remote hobby shop via eBay.
These tires have a much larger diameter than the original tires, which means
that the motor-to-pavement system now increased speed and reduced torque;
the exact opposite of what I want. However, the tires look great and seem
to have a pretty good grip for on and off-road situations.

Argonaut uses Ackerman steering, so only needs one motor to drive. Instead
of the ancient electronic speed control that was used on the vehicle for RC
purposes, I opted for a robotics motor driver. Many such drivers are available,
so I had to whittle down the options to make a decision. I wanted at least
3 amps of current continuosly, 8-bit or more of PWM control and electronic
braking is a plus. I did NOT want a serial or RC command interface.